TW201537805A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

The purpose of the present invention is to provide a non-aqueous electrolyte secondary battery that has excellent long-term cycle characteristics. This objective can be achieved by the non-aqueous electrolyte secondary battery of the present invention, said non-aqueous electrolyte secondary battery comprising: (I) a positive electrode (a) that contains a positive electrode active substance that is represented by formula (1) and that contains an excess of lithium, or a positive electrode (b) that contains a positive electrode active substance that is represented by formula (2) and a lithium-containing oxide in which the charge/discharge potential is 3.3 V or less with respect to counter electrode lithium and the average discharge voltage above 3.3 V is 3.4-5.0 V; and (II) a negative electrode that contains a graphitizable or non-graphitizable carbonaceous material in which the average layer spacing (d002) of the (002) plane as determined by X-ray diffraction is 0.345-0.400 nm, the crystallite size Lc(002) in the c-axis direction is 1.0-20.0 nm, the specific surface area is 1-50 g/m2, the butanol true density ([rho]BtOH) is 1.45-2.20 g/cm3, and the elemental sulfur content is 75-3,500 [mu]g/g.

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a nonaqueous electrolyte secondary battery. According to the present invention, a nonaqueous electrolyte secondary battery having reduced electrical resistance during discharge and excellent cycle capacity retention can be obtained.

In recent years, people have been paying more and more attention to environmental issues. Therefore, the industry is studying how to install large-scale lithium ion secondary batteries with high energy density and excellent output characteristics on electric vehicles. Since the capacity per unit volume becomes important in the use of small mobile devices such as mobile phones and notebook computers, graphite materials having a relatively high density are mainly used as negative electrode active materials. However, when a lithium ion secondary battery for a vehicle is used, it is difficult to exchange in the middle because of its large size and high price. Therefore, it must have at least the same durability as a car, and it is required to have a life performance (high durability) of more than 10 years. When a graphite material or a carbonaceous material having a developed graphite structure is used, the crystal is expanded and shrunk due to repeated doping and dedoping of lithium, and the crystal is easily broken, and the repeatability of charge and discharge is poor, so it is not suitable for the requirement. Anode material for lithium ion secondary batteries for automotive use with high cycle durability. In contrast, although the easily graphitizable carbon is due to the developed proportion of the crystal structure There is a difference, but compared with the graphite material, the expansion and shrinkage of the particles due to the doping and dedoping reaction of lithium is less. Since the expansion shrinkage of the non-graphitizable carbon is smaller than that of the easily graphitizable carbon, it is considered to have a high From the viewpoint of cycle durability, these carbonaceous materials are suitable for automotive use. However, in the initial charge and discharge of easily graphitizable carbon or non-graphitizable carbon, even charging (reaction of doping lithium into a carbonaceous material) cannot be discharged (reaction of dedoping lithium from a carbonaceous material) The so-called irreversible capacity (the capacity for subtracting the discharge capacity from the discharge capacity) is large, and an unnecessary positive electrode active material is required. Therefore, there is a problem that the energy density is lowered, and it is required to solve such problems and further improve the second. The performance of the secondary battery.

In order to improve the performance of lithium ion secondary batteries, attempts have been made to reduce irreversible capacity. During the first charging process, lithium desorbed from the positive electrode active material is embedded in the carbonaceous material (negative electrode active material) of the negative electrode. Lithium embedded in the carbonaceous material of the negative electrode is detached from the carbonaceous material during discharge and embedded in the positive electrode active material. One part of the lithium embedded in the carbonaceous material cannot be detached from the negative active material and remains in the carbonaceous material. Lithium remaining in the carbonaceous material cannot participate in charge and discharge, so the discharge capacity is reduced.

In order to prevent the decrease in the discharge capacity, there is known a method in which the positive electrode active material is excessively contained in lithium which is equivalent to lithium remaining in the carbonaceous material, and the loss due to the irreversible capacity is supplemented (Patent Document 1). . Further, another method is known which prevents lithium from being desorbed from lithium by a low voltage when the positive electrode contains a lithium compound, thereby preventing a decrease in discharge capacity (Patent Document 2).

[Practical Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 4-181860

[Patent Document 2] Japanese Patent Laid-Open No. Hei 6-342673

[Summary of the Invention] [Problems to be solved by the invention]

The initial battery capacity can be improved by a secondary battery comprising a positive electrode comprising a large amount of (positively) positive electrode active material containing lithium, and a negative electrode comprising a carbon negative electrode material as a negative electrode active material. However, the positive electrode active material having an excessive lithium content has a problem in that the electrochemical stability is poor in the charge and discharge cycle, and the battery capacity is lowered in the long-term charge and discharge cycle. Further, there is a problem in that not only the positive electrode is deteriorated, but also the transition metal of the positive electrode active material is eluted to the electrolytic solution during charging and discharging, and moves to the negative electrode side to cause a side reaction, resulting in a decrease in battery capacity or a decrease in safety.

An object of the present invention is to provide a nonaqueous electrolyte secondary battery excellent in long-term cycle characteristics.

The inventors of the present invention conducted intensive studies on a secondary battery having an excellent initial battery capacity and excellent long-term cycle characteristics, and finally surprisingly found that by combining a positive electrode containing a large amount of a positive electrode active material containing lithium or containing a low voltage. Lithium-deactivated lithium compound as a positive active material The positive electrode and the negative electrode including the carbonaceous material having a fixed sulfur content as the negative electrode active material can reduce the irreversible capacity of the secondary battery, have a high charge and discharge capacity, and suppress a decrease in battery capacity in the charge and discharge cycle (to achieve high capacity maintenance) rate).

The present invention has been developed in view of the above findings.

Accordingly, the present invention relates to: [1] A nonaqueous electrolyte secondary battery comprising: (I) a positive electrode comprising (a) a formula (1): A _{x + α} M _y B _β O _z-γ (1) (wherein, A is Li ⁺ , x is 1, 2, or 3, and α is 0 < α 1, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is 2, 3, or 4, γ is 0 γ 0.05) indicates a positive electrode active material, or contains (b) a formula (2): A _x M _y B _β O _z (2) (wherein A is Li ⁺ and x is 1, 2, or 3, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is a positive electrode active material represented by 2, 3, or 4), and a lithium-containing oxide having a charge and discharge potential for the opposite electrode lithium existing at 3.3 V or less and an average discharge voltage exceeding 3.3 V of 3.4 to 5.0 V And (II) a negative electrode comprising (002) average layer spacing d ₀₀₂ of 0.345 to 0.400 nm and a crystallite size of the c-axis direction Lc ₍₀₀₂₎ of 1.0 to 20.0 nm obtained by X-ray diffraction. , the specific surface area is 1~50g/m ² , the true density of butanol ρ _BtOH is 1.45~2.20g/cm ³ , and the easily graphitized or non-graphitizable carbonaceous material with sulfur content of 75~3500μg/g, [2 The non-aqueous electrolyte secondary battery according to [1], wherein the easily graphitizable carbonaceous material or the non-graphitizable carbonaceous material is a carbonaceous material made of pitch as a carbon source, or [3] a vehicle. The nonaqueous electrolyte secondary battery according to [1] or [2] is provided.

According to the nonaqueous electrolyte secondary battery of the present invention, it is possible to obtain a nonaqueous electrolyte secondary battery which is excellent in initial battery capacity and excellent in cycle characteristics over a long period of time. Since the nonaqueous electrolyte secondary battery of the present invention has excellent cycle characteristics, it can be effectively used in automobiles requiring long life and high input and output characteristics (for example, a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), And electric vehicles (EV) are equipped with power supplies.

The reason why the initial battery capacity of the nonaqueous electrolyte secondary battery of the present invention is excellent and the cycle characteristics are excellent in the long term is not completely described, but may be considered as follows. However, the invention is not limited to the following description.

A negative electrode made of a negative electrode active material (carbonaceous material) having the physical property, and a positive electrode containing an excess of lithium When the positive electrode of the substance or the positive electrode active material containing a lithium compound such as a lithium compound which is desorbed by a low voltage is added, an SEI (Solid Electrolyte Interface) film is formed on the surface of the negative electrode, the battery voltage is lowered. . Moreover, the reaction speed of electrons or ions and the activation energy vary, and the properties of the SEI of the surface of the negative electrode vary. Therefore, the SEI of the nonaqueous electrolyte secondary battery of the present invention has a low electric resistance, and can suppress an increase in the average discharge voltage of the battery and a decrease in the battery capacity at the time of charge and discharge cycles.

The positive electrode containing a positive electrode active material having an excessive lithium content has a problem that the structure is unstable, and the transition metal oxide is eluted into the electrolytic solution during charge and discharge, and moves toward the negative electrode side to cause a side reaction. However, by containing a fixed amount of sulfur element in the negative electrode active material, sulfur acts as a catalyst, suppresses the side reaction, and suppresses a decrease in battery capacity at the time of charge and discharge cycles.

Fig. 1 is a charge and discharge potential diagram of a lithium ion secondary battery (A) to which a positive electrode containing a lithium oxide is added, and a lithium ion secondary battery (B) using a conventional positive electrode.

"Non-aqueous electrolyte secondary battery"

The nonaqueous electrolyte secondary battery of the present invention comprises: (I) a positive electrode comprising (a) a formula (1): A _{x + α} M _y B _β O _z-γ (1) (wherein A is Li ⁺ , x is 1, 2, or 3, and α is 0 < α 1, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is 2, 3, or 4, γ is 0 γ 0.05) indicates a positive electrode active material, or contains (b) a formula (2): A _x M _y B _β O _z (2) (wherein A is Li ⁺ and x is 1, 2, or 3, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is a positive electrode active material represented by 2, 3, or 4), and a lithium-containing oxide having a charge and discharge potential for the opposite electrode lithium existing at 3.3 V or less and an average discharge voltage exceeding 3.3 V of 3.4 to 5.0 V And (II) a negative electrode comprising (002) average layer spacing d ₀₀₂ of 0.345 to 0.400 nm and a crystallite size of the c-axis direction Lc ₍₀₀₂₎ of 1.0 to 20.0 nm obtained by X-ray diffraction. An easily graphitizable or non-graphitizable carbonaceous material having a specific surface area of 1 to 50 g/m ² , a butanol true density ρ _BtOH of 1.45 to 2.20 g/cm ³ , and a sulfur element content of 75 to 3500 μg/g.

"positive electrode"

As one of the positive electrode types, it contains the general formula (1) A lithium-containing chalcogenide (hereinafter referred to as a lithium excess chalcogenide), a binder (adhesive), a conductive material, and a current collector, which have an excessive lithium content.

Further, as another mode of the positive electrode, the lithium-containing chalcogen compound represented by the formula (2), the lithium-containing oxide, the conductive material, and the current collector are contained.

(Lithium excess chalcogenide)

The lithium excess chalcogenide used in the present invention is not particularly limited as long as it contains lithium excessively, but may be exemplified by a lithium-containing chalcogenide having a layered structure and a lithium-containing chalcogen compound having an olivine structure. Or lithium-containing chalcogenide having a spinel structure excessively containing lithium.

The lithium-containing chalcogenide compound having a layered structure has a layered structure and is represented by LiMO ₂ , and M represents a part of a transition metal and a transition metal substituted by a heterogeneous transition metal, an alkaline earth metal, or aluminum. Specifically, a transition of a different element such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ or LiNi _x Co _y Mn _z O ₂ (where x, y, and z represent composition ratios, x+y+z=1) may be mentioned. Part of the metal.

Further, the lithium-containing chalcogenide compound having an olivine structure has an olivine structure and is represented by LiMPO ₄ or Li ₂ MSiO ₄ , and M represents a transition metal of a heterogeneous transition metal, an alkaline earth metal, or an aluminum, and a transition metal portion. By. Specific examples thereof include LiFePO ₄ , LiCoPO ₄ , LiVPO ₄ , LiVPO ₄ F, LiMnPO ₄ , LiMn _7/8 Fe _1/8 PO ₄ , LiNiVO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , LiFeP ₂ O ₇ , Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₂ CoSiO ₄ , Li ₂ MnSiO ₄ , Li ₂ FeSiO ₄ , LiNi _x Co _y Mn _z PO ₄ , or Li ₂ Ni _x Co _y Mn _z SiO ₄ (where x, y, and z represent the composition ratio, x + y + z = 1), the part of the transition metal is replaced by a heterogeneous element.

Further, the lithium-containing chalcogenide compound having a spinel structure has a spinel structure and is represented by LiM ₂ O ₄ , and M represents a portion in which a transition metal, an alkaline earth metal, an aluminum-substituted transition metal, and a transition metal are substituted. Specifically, for example, LiMn ₂ O ₄ , LiCo ₂ O ₄ , LiFe ₂ O ₄ , or LiNi _x Co _y Mn _z O ₄ (where x, y, and z represent composition ratios, x+y+z=2 Part of the transition metal is replaced by a heterogeneous element.

The lithium excess chalcogenide is not limited, but preferably has a layered structure of a lithium excess chalcogenide or a lithium excess chalcogenide having a spinel structure, and more preferably a lithium excess chalcogen having a spinel structure. Compound. The reason for this is that the structural stability is high and the reversible reaction can be maintained for a long period of time.

The lithium excess chalcogenide used in the present invention is doped (embedded) with lithium ions to a lithium-containing chalcogenide having the layered structure, a lithium-containing chalcogen compound having an olivine structure, or having a spinel structure. Among lithium-containing chalcogenides. The doping of lithium ions can be carried out by a well-known method, and an electrochemical method or a chemical method can be used.

The electrochemical method is not limited, but the following method can be used. A positive electrode is produced by adding a conductive material and a binder to the lithium-containing chalcogenide having a layered structure, a lithium-containing chalcogenide having an olivine structure, or a lithium-containing chalcogenide having a spinel structure. Metal lithium was used as a counter electrode, and an electric current treatment was performed in a nonaqueous solvent to dope lithium in the positive electrode. By this method, a lithium excess chalcogenide having an excessive lithium ion content can be obtained.

The chemical method is not limited, but the following methods can be used. After the lithium-containing chalcogenide having a layered structure, a lithium-containing chalcogenide having an olivine structure, or a lithium-containing chalcogenide having a spinel structure is impregnated into a lithium compound solution, and doped with lithium ions, The heat treatment is carried out at 300 to 450 ° C as needed to obtain a lithium excess chalcogenide having an excessive lithium ion content. Examples of the lithium compound include organic compounds such as n-butyllithium, sec-butyllithium or t-butyllithium, and lithium salts such as lithium oxalate, lithium iodide or lithium nitrate. Doping is carried out using an aqueous solution of such a lithium organic compound or a lithium salt. When a lithium organic compound is used, for example, LiMO ₂ can be immersed in a solution, allowed to react, and then washed with a solvent, and used as a positive electrode active material. Further, when a lithium salt is used, LiMO _{2 is} immersed in a solution, and then heat-treated at 300 to 450 ° C, preferably at 300 to 400 ° C, and doped with lithium to obtain a lithium excess chalcogenide having an excessive lithium ion content. .

Alternatively, it can also be obtained by mixing a transition metal oxide and lithium hydride at an arbitrary ratio and baking in an atmospheric environment, for example, at 680 °C.

In the lithium excess chalcogen compound represented by the general formula (1), α is 0<α 1 is not limited, but the lower limit of α is preferably 0.04 or more, and particularly preferably 0.10 or more. The upper limit of α is preferably 0.30 or less, and more preferably 0.20 or less. In view of the fact that sufficient effect can be obtained, α is preferably 0.10 to 0.20.

In the lithium excess chalcogenide, M is a metal selected from the group consisting of a transition metal, an alkali metal, an alkaline earth metal, and aluminum, and is not particularly limited, and preferably, manganese (Mn) or cobalt is exemplified. Co), nickel (Ni), magnesium (Mg), aluminum (Al), iron (Fe), vanadium (V), molybdenum (Mo), copper (Cu), titanium (Ti), or chromium (Cr). y is 1 or 2.

In the lithium excess chalcogenide, B is P or Si, and β is 0. β 1. When B is P or Si, and β is 1, the lithium excess chalcogenide has a lithium-containing chalcogenide having an olivine structure. On the other hand, when β is 0, the lithium excess chalcogenide has a lithium-containing chalcogenide having a layered structure or a lithium-containing chalcogenide having a spinel structure.

In the lithium excess chalcogenide, z is 2, 3, or 4, and γ is 0. γ 0.05. When z is 2 or 3, the lithium excess chalcogenide is a lithium excess chalcogenide having a layered structure, and when z is 4, the lithium excess chalcogenide is a lithium excess chalcogenide having a spinel structure.

(Lithium-containing chalcogenide)

The lithium-containing chalcogen compound represented by the formula (2) is not particularly limited, and specific examples thereof include the lithium-containing chalcogen compound having a layered structure, a lithium-containing chalcogen compound having an olivine structure, or A lithium-containing chalcogenide having a spinel structure.

In the lithium-containing chalcogenide, M is a metal selected from the group consisting of a transition metal, an alkali metal, an alkaline earth metal, and aluminum, and is not particularly limited, and preferred examples thereof include manganese (Mn) and cobalt (managed). Co), nickel (Ni), magnesium (Mg), aluminum (Al), iron (Fe), vanadium (V), molybdenum (Mo), copper (Cu), titanium (Ti), or chromium (Cr). y is 1 or 2.

In the lithium-containing chalcogenide, B is P or Si, and β is 0. β 1. When B is P or Si, and β is 1, the lithium-containing chalcogenide compound has a lithium-containing chalcogen compound having an olivine structure. On the other hand, when β is 0, the lithium-containing chalcogenide compound has a lithium-containing chalcogen compound having a layered structure or a lithium-containing chalcogen compound having a spinel structure.

In the lithium-containing chalcogenide, z is 2, 3, or 4. When z is 2 or 3, the lithium-containing chalcogenide is a lithium-containing chalcogenide having a layered structure, and when z is 4, the lithium-containing chalcogenide is a lithium-containing chalcogenide having a spinel structure.

(containing lithium oxide)

The lithium-containing oxide has a charge and discharge potential for the counter electrode lithium of 3.3 V or less, and an average discharge voltage of more than 3.3 V is 3.4 to 5.0 V. That is, it is preferred that the lithium is dedoped and embedded in the negative electrode before the main positive electrode active material (containing lithium-containing chalcogenide) contained in the positive electrode. As shown in Fig. 1(A), when the positive electrode of the present invention containing a lithium-containing oxide is used, the charge and discharge potential is present at 3.3 V or less. Therefore, before the lithium-containing chalcogenide is contained, lithium ions are released to form SEI. Therefore, the irreversible capacity of the lithium-containing chalcogenide can be reduced. On the other hand, as shown in Fig. 1(B), when a conventional positive electrode is used, the charge and discharge potential does not exist at 3.3 V or less, and Li containing a lithium chalcogenide is consumed in the formation of SEI, and a lithium-containing chalcogenide is used. The irreversible capacity will increase.

Examples of the lithium-containing oxide include Li _x MO _y , (M is a transition metal such as Mo, Mn, Co, Ni, and Fe), a lithium manganese composite oxide such as TiS ₂ or LiMn ₃ O ₆ , and have 2 to 3 V. (potential to Li/Li ⁺ ), etc. Further, Li ₃ FeF ₆ , LiNiOF, or Li ₂ FeO ₂ F containing fluorine may also be used.

Examples of the Li _x MO _y include Li ₂ MoO ₃ , Li ₂ Mn ₂ O ₄ , Li ₂ NiO, Li ₂ NiO _3-a , and Li _1+a Ni _1-a O ₂ (Li/Ni ratio is greater than 1). LiNiO ₂ ), Li ₆ CoO ₄ , Li ₂ CoSiO ₄ , LiCuO, Li ₆ Mo ₂ O, Li ₉ TiN ₃ O ₂ , Li ₈ CoO ₆ , Li ₆ Fe ₂ O ₃ , Li ₅ Fe ₂ O ₃ , Li ₃ Fe ₂ O ₃ , Li ₂ FeO ₂ , or Li ₂ Fe ₂ O ₃ .

The lithium-containing oxide active material preferably has a capacity larger than that of the lithium-containing chalcogen compound contained in the positive electrode. This property is determined by the relationship between the lithium-containing oxide active material and the lithium-containing chalcogenide contained in the positive electrode. Therefore, it is preferred to use the lithium-containing oxide active material in association with the lithium-containing chalcogenide. Containing lithium oxide.

Preferably, the amount of Li intercalation of the carbonaceous material corresponding to the negative electrode determines the amount of the lithium-containing oxide contained in the positive electrode, for example, 0.04 to 1.00 in the case of the Mo number of Li, and more preferably 0.10 to 0.20.

(collector)

As the current collector for the positive electrode, various materials which have been conventionally used or have been proposed can be used. For example, a metal material such as aluminum, stainless steel, nickel plating, titanium, or tantalum, or a carbon material such as carbon cloth or carbon paper may be mentioned, but a metal material is preferable, and aluminum is particularly preferable.

(adhesive (adhesive))

The adhesive used for the positive electrode is not particularly limited as long as it does not react with the electrolytic solution, and examples thereof include polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP). , polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), ethylene-propylene-diene copolymer (EPDM), fluororubber (FR), acrylonitrile-butadiene rubber (NBR) ), sodium polyacrylate, propylene or carboxymethyl cellulose (CMC), and the like. These adhesives may be used singly or in combination of two or more kinds in an appropriate ratio.

The content of the binder is not particularly limited, but is preferably 0.1% by mass or more based on the substance contained in the positive electrode (herein, the amount of the positive electrode active material + the amount of the adhesive + the amount of the conductive material = 100% by weight). It is preferably 0.5% by mass or more, particularly preferably 1.0% by mass or more, and most preferably 1.5% by mass or more. The upper limit is preferably 8.0% by mass or less, more preferably 6.0% by mass or less, particularly preferably 4.0% by mass or less, and most preferably 3.0% by mass or less based on the substance contained in the positive electrode. Since the content of the binder is 0.1 to 8.0% by mass, it is possible to maintain a good bond between the current collector foil and the particles, and to suppress an increase in resistance due to the binder.

(conductive additive)

As the conductive auxiliary agent for the positive electrode, various materials which have been conventionally used or have been proposed can be used. For example, a metal material such as copper or nickel, a graphite material such as natural graphite or artificial graphite, a carbon black such as acetylene black, or an amorphous carbonaceous material such as needle coke may be mentioned. These conductive auxiliary agents may be used singly or in combination of two or more kinds in an appropriate ratio.

The content of the conductive auxiliary agent is not particularly limited, but is preferably 0.01% by mass or more based on the substance contained in the positive electrode (herein, the mass of the positive electrode active material + the amount of the adhesive agent + the amount of the conductive auxiliary agent = 100% by weight). It is preferably 0.05% by mass or more, particularly preferably 0.1% by mass or more, and most preferably 1% by mass or more. The upper limit is preferably 5.0% by mass or less, more preferably 4.0% by mass or less, particularly preferably 3.5% by mass or less, and most preferably 3.0% by mass or less based on the substance contained in the positive electrode. Because the content of conductive additive is 0.01 to 5.0% by mass, so it is possible to suppress the decrease in capacity and reduce the electric resistance.

(solvent)

When a positive electrode is produced, a solvent is added to the positive electrode active material, the adhesive, and the conductive auxiliary agent to carry out kneading. The solvent used in the production of the positive electrode for a nonaqueous electrolyte secondary battery is not limited. For example, water, a mixed solvent of an alcohol and water, etc. are mentioned. Further, examples of the organic solvent include aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, toluene, xylene or methylnaphthalene, heterocyclic compounds such as quinoline or pyridine, and acetone and methyl b. Ketones such as ketone or cyclohexanone, esters such as methyl acetate or methyl acrylate, amines such as diethylenetriamine or N,N-dimethylaminopropylamine, diethyl ether, propylene oxide or tetrahydrofuran (THF), etc. An amine, an amine such as N-methylpyrrolidone (NMP), dimethylformamide or dimethylacetamide, or a polar aprotic solvent such as hexamethylphosphonium or dimethyl hydrazine. .

"Negative Electrode"

The negative electrode used in the present invention contains the (002) average layer spacing d ₀₀₂ of 0.345 to 0.400 nm and the crystallite size Lc ₍₀₀₂₎ of the c-axis direction of 1.0 to 20.0 nm, which is obtained by X-ray diffraction. An easily graphitizable or non-graphitizable carbonaceous material having a surface area of 1 to 50 g/m ² , a butanol true density ρ _BtOH of 1.45 to 2.20 g/cm ³ , and a sulfur element content of 75 to 3500 μg/g is used as a negative electrode active material. The negative electrode usually contains a binder (adhesive) and a current collector in addition to the negative electrode active material. Further, a conductive auxiliary agent may be contained as needed.

(butanol true density)

The true density of the graphite material having the desired structure is 2.2 g/cm ³ , and there is a tendency that the true density will become smaller as the crystal structure is disordered. Therefore, true density can be used as an indicator of the structure of carbon. The carbonaceous material used in the present invention has a true density of butanol of 1.45 to 2.15 g/cm ³ , and the carbonaceous material in the range of 1.70 to 2.15 g/cm ³ is referred to as an easily graphitizable carbon, which will be 1.45 to 1.70. The g/cm ³ is called non-graphitizable carbon. When an easily graphitizable carbonaceous material is used, the true density is 1.70 to 2.15 g/cm ³ , and particularly preferably 1.90 to 2.15 g/cm ³ . On the other hand, when a non-graphitizable carbonaceous material is used, the true density is 1.45 to 1.70 g/cm ³ , and particularly preferably 1.45 to 1.65 g/cm ³ . When the true density of the carbonaceous material is too large, the number of pores capable of accommodating lithium is small, and the doping and dedoping capacity are small, which is not preferable. In addition, since the increase in true density is accompanied by the selective orientation of the carbon hexagonal mesh surface, the carbonaceous material often expands and contracts when doping or dedoping lithium, which is not preferable. On the other hand, when the true density of the carbon material is less than 1.45 g/cm ³ , the closed cells often occur, and the doping and dedoping capacities are reduced, which is not preferable. Further, since the electrode density is lowered, the volume energy density is lowered, which is not preferable.

The higher the crystal completeness, the smaller the value of the average layer spacing of the (002) plane of the carbonaceous material. In the ideal graphite structure, the average layer spacing of the (002) plane of the carbonaceous material is 0.3354 nm, and the structure exists. The more disordered, the more the value will increase. Therefore, the average layer spacing is effective as an indicator indicating the structure of carbon. The carbonaceous material of the present invention is an easily graphitizable carbonaceous material or a non-graphitizable carbonaceous material, and the (002) plane is measured by an X-ray diffraction method. The average layer spacing is 0.345 nm or more and 0.40 nm or less, and particularly preferably 0.365 nm or more and 0.400 nm or less. Particularly preferred is 0.375 nm or more and 0.400 nm or less. In the case of a graphitizable carbonaceous material, the average layer spacing of the (002) plane measured by the X-ray diffraction method is 0.345 nm or more and 0.365 nm or less, and particularly preferably 0.345 nm or more and 0.360 nm or less. On the other hand, in the case of a non-graphitizable carbonaceous material, the average layer spacing of the (002) plane measured by the X-ray diffraction method is 0.365 nm or more and 0.40 nm or less, and particularly preferably 0.370 nm or more and 0.400 nm or less. Particularly preferred is 0.375 nm or more and 0.400 nm or less. Since the cycle characteristics can be improved, a non-graphitizable carbonaceous material having an average layer spacing of 0.365 nm or more is preferred. That is, when a non-graphitizable carbonaceous material is used as a negative electrode, the durability of lithium doping and dedoping reaction is excellent. In other words, the non-graphitizable carbonaceous material has a small expansion shrinkage at the time of charge and discharge as compared with graphite, and is excellent in repeatability (so-called durability).

The size Lc ₍₀₀₂₎ of the crystallites in the c-axis direction of the carbonaceous material used in the present invention is 1.0 to 20.0 nm, preferably 1.0 to 10 nm, and more preferably 1.0 to 5.0 nm. When Lc _{(002) is} too large, the occlusion hole will increase, the doping/de-doping capacity will decrease, or the graphite material may be collapsed or the electrolyte is decomposed due to doping/dedoping of the active material, so it is not preferable. . On the other hand, when Lc _{(002) is} too small, the formation of a carbon skeleton is not sufficient, and thus it is not preferable.

The carbonaceous material used in the present invention has a BET specific surface area of from 1 to 50 m ² /g, preferably from 1 to 10 m ² /g. When the BET specific surface area exceeds 50 m ² /g, when it is used as a negative electrode of a nonaqueous electrolyte secondary battery, the decomposition reaction with the electrolytic solution increases, and an irreversible capacity increases, so that battery performance is lowered. On the other hand, when the BET specific surface area is less than 1 m ² /g, when it is used as a negative electrode of a nonaqueous electrolyte secondary battery, the input/output characteristics may be lowered due to a decrease in the reaction area with the electrolytic solution.

The carbonaceous material used in the present invention contains sulfur element 75 to 3500 μg/g. The lower limit of the sulfur element content of the carbonaceous material is preferably 80 μg/g or more, more preferably 90 μg/g or more, particularly preferably 100 μg/g or more, and most preferably 110 μg/g or more. The upper limit of the sulfur element content of the carbonaceous material is preferably 3000 μg / g or less, more preferably 2500 μg / g or less, particularly preferably 2000 μg / g or less, particularly preferably 1500 μg / g or less, and most preferably 1000 μg. /g below. Since the sulfur element content is from 75 to 3,500 μg/g, it is possible to suppress the problem that the transition metal oxide eluted into the electrolytic solution during the charge and discharge moves to the negative electrode side and causes a side reaction by the action of the catalyst of sulfur. Therefore, it is possible to improve the long-term cycle characteristics.

As the carbon source for producing the carbonaceous material, an easily graphitizable carbonaceous material or a non-graphitizable carbonaceous material made of a thermosetting resin or a thermoplastic resin containing a sulfur element can be used as the negative electrode active material of the present invention. Further, when a thermosetting resin or a thermoplastic resin containing no sulfur element is used, an easily graphitizable carbonaceous material or a non-graphitizable carbonaceous material prepared by mixing a resin having an appropriate amount of sulfur or a sulfur-containing resin may be used. It is a negative electrode active material of this invention. Further, although petroleum or coal which is a raw material such as petroleum pitch or coal pitch contains sulfur, the content of sulfur varies greatly depending on the place of production. In addition, since petroleum will be desulfurized during its refining process, the sulfur content of petroleum asphalt or coal tar pitch will also vary greatly. Therefore, an easily graphitizable carbonaceous material or a non-graphitizable carbonaceous material usable in the present invention can be produced by using petroleum pitch or coal pitch having the best sulfur content. However, the use of petroleum tar with a high sulfur content, etc. At the time, desulfurization can be carried out to obtain a carbonaceous material having the best sulfur content. Further, when petroleum pitch or the like having a low sulfur content is used, it is possible to obtain a carbonaceous material having an optimum sulfur content by adding an appropriate amount of sulfur.

The carbonaceous material used in the present invention has a Li-NMR of 25 to 130 ppm. When using an easily graphitizable carbonaceous material, Li-NMR is 10 to 40 ppm, and particularly preferably 25 to 40 ppm. On the other hand, when a non-graphitizable carbonaceous material is used, Li-NMR is 55 to 130 ppm, and particularly preferably 80 to 120 ppm. Since the Li-NMR of the easily graphitizable carbonaceous material is 10 to 40 ppm and the Li-NMR of the non-graphitizable carbonaceous material is 55 to 130 ppm, the rapid charge and discharge performance is excellent.

The average particle diameter of the carbonaceous material used in the present invention is not particularly limited, but is preferably 3 to 50 μm, more preferably 3 to 30 μm, and particularly preferably 3 to 10 μm. In order to improve the output characteristics in the performance of the nonaqueous electrolyte secondary battery, it is important to reduce the thickness of the active material layer of the electrode and to lower the electric resistance. Further, when the average particle diameter is 50 μm or less, the lithium diffusion length in the particles is shortened, which is preferable in the case of rapid charging.

The carbon source of the easily graphitizable carbonaceous material is not particularly limited, and examples thereof include petroleum pitch or tar, coal pitch or tar, or a thermoplastic resin. Examples of the thermoplastic resin include polyacetal, polyacrylonitrile, styrene/divinylbenzene copolymer, polyimide, polycarbonate, modified polyphenylene ether, polyterephthalic acid, polyarylate, and poly Bismuth, polyphenylene sulfide, fluororesin, polyamine-limonamide, polyether ketone ether, or polyvinyl chloride.

The carbon source of the non-graphitizable carbonaceous material is not particularly limited, and examples thereof include petroleum pitch or tar, coal pitch or tar, thermoplastic resin, or heat. Curable resin. Examples of the thermoplastic resin include polyacetal, polyacrylonitrile, styrene/divinylbenzene copolymer, polyimide, polycarbonate, modified polyphenylene ether, polyterephthalic acid, polyarylate, and poly Bismuth, polyphenylene sulfide, fluororesin, polyamine-limonamide, polyether ketone ether, or polyvinyl chloride. Further, examples of the thermosetting resin include polyimine, phenol resin, amino resin, unsaturated polyester resin, diallyl phthalate resin, alkyd resin, epoxy resin, and urethane resin. Further, when petroleum pitch or tar or the like and a thermoplastic resin are used as the carbon source, it is necessary to insolubilize the carbon sources by oxidation treatment.

(Manufacture of carbonaceous materials by tar or asphalt)

Hereinafter, a method of producing the non-graphitizable carbonaceous material of the present invention by tar or pitch will be exemplified.

First, the cross-linking treatment (non-melting) performed by the tar or the asphalt is aimed at hardly graphitizing the carbonaceous material obtained by carbonizing the cross-linked tar or pitch. Further, when the crosslinking treatment is not carried out or the crosslinking treatment is weak, an easily graphitizable carbonaceous material can be obtained. As tar or bitumen, petroleum or coal tar or bitumen, such as petroleum tar or bitumen which is copied during the production of ethylene, coal tar produced during the dry distillation of coal, and heavy group after distillation of the low boiling point component of coal tar can be used. A tar or bitumen obtained by liquefaction of bitumen or coal. Further, two or more types of tar and pitch may be mixed.

As mentioned above, the sulfur content of petroleum and coal will vary greatly depending on the origin. Therefore, by performing a desulfurization treatment when using a bitumen or the like having a large sulfur content, a sulfur compound is added when a bitumen having a low sulfur content or the like is used, and a carbonaceous material having an appropriate sulfur content can be obtained.

Specifically, examples of the method of not melting include a method using a crosslinking agent or a method using a oxidizing agent such as air. When a crosslinking agent is used, a petroleum tar or a bitumen or a coal tar or a pitch-adding crosslinking agent is heated and mixed to promote a crosslinking reaction to obtain a carbon precursor. For example, as the crosslinking agent, divinylbenzene, trivinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, or N, N which is crosslinked by a radical reaction can be used. a polyfunctional vinyl monomer such as methylenebis acrylamide. The crosslinking reaction of the polyfunctional vinyl monomer can start the reaction by adding a radical initiator. As the radical initiator, α,α' azobisisobutyronitrile (AIBN), benzammonium peroxide (BPO), laurel peroxide, cumene hydroperoxide, 1-hydroperoxide butyl can be used. Or hydrogen peroxide, etc.

Further, when the treatment is carried out by an oxidizing agent such as air to promote the crosslinking reaction, it is preferred to obtain a carbon precursor by the following method. In other words, an aromatic compound having a boiling point of 200 ° C or more and a 2- to 3-ring aromatic compound or a mixture thereof is added as an additive to petroleum or coal-based pitch, and the mixture is heated and mixed, followed by molding to obtain an asphalt molded body. Next, an additive is extracted and removed from the asphalt shaped body by using a solvent having low solubility to the pitch and high solubility to the additive to form a porous pitch, which is then oxidized using an oxidizing agent to obtain a carbon precursor. The purpose of the aromatic additive is to extract and remove the additive from the formed asphalt molded body, to make the molded body porous, to easily perform a crosslinking treatment by oxidation, and to make the carbonaceous material obtained by carbonization porous. The additive may be selected, for example, from one or a mixture of two or more of naphthalene, methylnaphthalene, phenylnaphthalene, benzylnaphthalene, methylhydrazine, phenanthrene, or biphenyl. The amount of the aromatic additive added is preferably 100 parts by weight of the asphalt. 30 to 70 parts by weight.

In order to achieve uniform mixing, the asphalt and the additive are mixed in a state of being heated and melted. In order to easily extract the additive from the mixture, it is preferred to form a mixture of the pitch and the additive into particles having a particle diameter of 1 mm or less and then work. The molding may be carried out in a molten state, or may be carried out by cooling the mixture and then pulverizing it. As a solvent for extracting and removing an additive from a mixture of pitch and an additive, an aliphatic hydrocarbon such as butane, pentane, hexane or heptane, a mixture of an aliphatic hydrocarbon main body such as naphtha or kerosene, and methanol or ethanol may be used. Fatty alcohols such as propanol or butanol. By extracting the additive from the mixture of the pitch and the additive by using such a solvent, the additive can be removed from the molded body while maintaining the shape of the molded body. It is inferred that at this time, pores of the additive are formed in the formed body, and an asphalt molded body having uniform porosity can be obtained.

In order to crosslink the obtained porous pitch, followed by using an oxidizing agent, it is preferred to carry out oxidation at a temperature of from 120 to 400 °C. As the oxidizing agent, O ₂ , O ₃ , NO ₂ , a mixed gas which is diluted with air, nitrogen or the like, an oxidizing gas such as air, or an oxidizing liquid such as sulfuric acid, nitric acid or hydrogen peroxide water can be used. As the oxidizing agent, an oxygen-containing gas such as air or a mixed gas of air and another gas such as a combustion gas is oxidized at 120 to 400 ° C, and the method of performing the crosslinking treatment is simple and economically advantageous. At this time, if the softening point of the pitch is too low, the asphalt melts during oxidation and is difficult to be oxidized. Therefore, the softening point of the pitch to be used is preferably 150 ° C or higher.

By the carbon precursor which has been subjected to the crosslinking treatment as described above The carbonaceous material of the present invention can be obtained by performing preliminary calcination and then carbonizing at 900 ° C to 1600 ° C in a non-oxidizing gas atmosphere.

(Manufacture of carbonaceous materials by resin)

Hereinafter, a method of producing a non-graphitizable carbonaceous material by a thermosetting resin will be described as an example.

The carbonaceous material used in the present invention is obtained by using a sulfur-containing resin as a precursor, or by carbonization at 900 ° C to 1600 ° C. When a sulfur-free resin is used, in order to obtain a carbonaceous material having a suitable sulfur content, a sulfur compound (for example, polyphenylene sulfide resin or polyfluorene) is preferably added.

As the resin, a thermosetting resin such as a phenol resin or a furan resin or a functional group of the resin may be partially modified. The carbonaceous material can also be obtained by subjecting the thermosetting resin to preliminary calcination at a temperature of 900 ° C or lower, followed by pulverization, and carbonization at 900 ° C to 1600 ° C. In order to promote the curing of the thermosetting resin, promote the degree of crosslinking, or increase the carbonization yield, oxidation treatment (non-melting treatment) may be carried out at a temperature of 120 to 400 ° C as needed. As the oxidizing agent, O ₂ , O ₃ , NO ₂ , a mixed gas which is diluted with air, nitrogen or the like, an oxidizing gas such as air, or an oxidizing liquid such as sulfuric acid, nitric acid or hydrogen peroxide water can be used. Although the pulverization step can be carried out after carbonization, the carbon precursor is hardened after the carbonization reaction, and it is difficult to control the particle size distribution after the pulverization. Therefore, it is preferable to pulverize at 900 ° C or lower before the preliminary firing. Process.

Further, a carbon precursor which has been subjected to an infusibilization treatment with a thermoplastic resin such as polyacrylonitrile or a styrene/divinylbenzene copolymer can also be used. The monomer mixture can be made into a minute by, for example, adding a monomer mixture in which a radical polymerizable vinyl monomer and a polymerization initiator are mixed to an aqueous dispersion medium containing a dispersion stabilizer, and suspending it by stirring and mixing. After the droplets, the radical polymerization is then promoted by raising the temperature to obtain the resins. The crosslinked structure can be developed by the infusible treatment, whereby the obtained resin is made into a spherical carbon precursor. The oxidation treatment is preferably carried out in a temperature range of 120 to 400 ° C, particularly preferably in the range of 170 ° C to 350 ° C, and particularly preferably in the temperature range of 220 to 350 ° C. As the oxidizing agent, O ₂ , O ₃ , SO ₃ , NO ₂ , a mixed gas which is diluted with air, nitrogen or the like, an oxidizing gas such as air, or an oxidizing property such as sulfuric acid, nitric acid or hydrogen peroxide water can be used. liquid. Then, the carbon precursor of the present invention can be obtained by preliminary calcining the carbon precursor which is infusible by heat, and then pulverizing it in a non-oxidizing gas atmosphere at 900 ° C to 1600 ° C to obtain the carbonaceous material of the present invention. material. Although the pulverization step can be carried out after carbonization, the carbon precursor is hardened after the carbonization reaction, and it is difficult to control the particle size distribution after the pulverization. Therefore, it is preferable to pulverize at 900 ° C or lower before the preliminary firing. Process.

(collector)

As the current collector for the negative electrode, various materials which have been conventionally used or have been proposed can be used. For example, a metal material such as copper, nickel, stainless steel or nickel-plated steel may be mentioned, but copper is preferred from the viewpoint of easiness of processing and cost.

(adhesive (adhesive))

The adhesive which can be used for the negative electrode is not particularly limited as long as it does not react with the electrolytic solution, and examples thereof include polyvinylidene fluoride. (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), ethylene-propylene-diene copolymer (EPDM) ), fluororubber (FR), acrylonitrile-butadiene rubber (NBR), sodium polyacrylate, propylene or carboxymethyl cellulose (CMC).

(solvent)

When the negative electrode for a non-aqueous electrolyte secondary battery of the present invention is produced, a solvent is added to the non-graphitizable carbonaceous material, a binder, or the like, and kneaded. The solvent used in the production of the negative electrode for a nonaqueous electrolyte secondary battery is not limited. Specifically, N-methylpyrrolidone (NMP) is mentioned. For example, in the case of polyvinylidene fluoride, a polar solvent such as N-methylpyrrolidone (NMP) is preferably used, but an aqueous emulsion such as SBR may also be used.

"Non-aqueous solvent electrolyte"

As the nonaqueous solvent type electrolyte, various materials which have been conventionally used or have been proposed can be used. As the nonaqueous solvent, for example, propylene carbonate, ethyl carbonate, dimethyl carbonate, diethyl carbonate, dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2 may be used. One type or two or more types of organic solvents such as methyltetrahydrofuran, cyclobutane or 1,3-dioxolane are used in combination. Further, as the electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiBOB, LiB(C ₆ H ₅ ) ₄ , or LiN(SO ₃ CF ₃ ) ₂ or the like can be used. In general, the positive electrode and the negative electrode can be permeable to each other through a permeable separator made of a nonwoven fabric or another porous medium, and immersed in an electrolytic solution to form a secondary battery.

"Splitter"

As the separator, a permeable separator composed of a nonwoven fabric and other porous media, which is generally used for a secondary battery, can be used. Alternatively, a separator or a solid electrolyte composed of a polymer gel impregnated with an electrolyte may be used together with the separator.

"Manufacture of Nonaqueous Electrolyte Secondary Battery"

An example of a method of producing a nonaqueous electrolyte secondary battery will be described below.

The lithium excess chalcogenide or the lithium-containing chalcogenide compound and the lithium-containing oxide are used as the positive electrode active material in the positive electrode. A suitable adhesive is molded together with a conductive auxiliary agent or the like for imparting conductivity to the electrode, and a layer is formed on the conductive collector. Specifically, an electrode mixture paste is prepared by adding an appropriate amount of a binder (adhesive) and a suitable solvent to the positive electrode active material. After it is coated/dried on a conductive current collector made of a circular or rectangular metal plate or the like, press molding is performed. Alternatively, the electrode mixture paste may be coated/dried on a conductive collector material, subjected to press forming, and punched into a circular or rectangular shape. Thus, a layer having a thickness of 10 to 200 μm was formed and used as a positive electrode.

The negative electrode may be used as it is, or may be used together with a conductive auxiliary agent such as 1-10% by weight of acetylene black or conductive carbon black. An electrode mixture paste is prepared by adding an appropriate amount of a binder (adhesive) and a suitable solvent and kneading. Then, it is applied/dried on a conductive collector material composed of, for example, a circular or rectangular metal plate, and then subjected to press forming. Forming a layer having a thickness of 10 to 200 μm and using it as a negative electrode for the electrode In production.

The positive electrode and the negative electrode which are formed as described above are allowed to pass through a permeating separator composed of a nonwoven fabric and another porous medium as needed, and are immersed in an electrolytic solution to form a secondary battery.

[2] Vehicle

The nonaqueous electrolyte secondary battery of the present invention is suitably used for a battery (typically a nonaqueous electrolyte secondary battery for vehicle driving) mounted on a vehicle such as an automobile.

The vehicle to which the present invention is used may be a well-known electric vehicle or a hybrid vehicle of a fuel cell and an internal combustion engine, and the like, but has a power supply device having at least the above-described battery, and is driven by power supply from the power supply device. The electric drive mechanism and the control device for controlling the same. Further, a mechanism including a power generating brake or a regenerative brake, converting energy generated by braking into electric energy, and charging the nonaqueous electrolyte secondary battery may be provided.

[Examples]

Hereinafter, the present invention will be specifically described by examples, but the examples are not intended to limit the scope of the invention.

<<Pressure Active Material Production Example 1>>

In this production example, spinel LiMn ₂ O _{4 was} synthesized.

Lithium hydride (LiOH) and manganese oxide (Mn ₃ O ₄ ) were mixed so that the lithium:manganese atom ratio was 1:2. The mixture was heat treated in an electric furnace at 750 ° C for 24 hours. After cooling the obtained fired product, it was pulverized again, and heat-treated at 850 ° C for 6 hours to obtain a positive electrode active material 1.

<<Pressure Active Material Production Example 2>>

In this production example, LiCoO _{2 was} synthesized.

Lithium hydride (LiOH) and cobalt oxide (Co ₃ O ₄ ) were mixed so that the lithium:cobalt atomic ratio was 1:1. The mixture was heat treated in an electric furnace at 750 ° C for 24 hours. After cooling the obtained fired product, it was pulverized again, and heat-treated at 850 ° C for 6 hours to obtain a positive electrode active material 2 .

<<Pressure Active Material Production Example 3>>

In the present production example, Li ₂ Mn ₂ O _{4 was} synthesized.

Lithium hydride (LiOH) and manganese dioxide (MnO ₂ ) were mixed so that the lithium:manganese atom ratio was 1:1. The mixture was heat-treated at 680 ° C for 48 hours in an electric furnace to obtain a cathode active material 3.

<<Pressure Active Material Production Example 4>>

In the present production example, Li _1.2 Mn ₂ O _{4 was obtained} .

The positive electrode active material 1 obtained by the positive electrode active material production example 1 and the positive electrode active material 3 obtained in the positive electrode active material production example 3 were mixed at 4:1 to obtain a positive electrode active material 4.

<<Pressure Active Material Production Example 5>>

In the present production example, Li _1.2 Mn ₂ O _{4 was} produced by an electrochemical synthesis method.

The lithium metal electrode and the positive electrode electrode prepared using the positive electrode active material 1 were immersed in an electrolytic solution, and discharged at about 0.78 mAh to obtain a positive electrode active material 5.

<<Pressure Active Material Production Example 6>>

In this production example, Li _1.2 CoO _{2 was} produced by an electrochemical synthesis method.

The lithium metal electrode and the positive electrode electrode prepared using the positive electrode active material 2 were immersed in an electrolytic solution, and discharged at about 0.75 mAh to obtain a positive electrode active material 6.

"Negative active material 1"

An easily graphitizable carbonaceous material having a sulfur content of 2480 μg/g was produced. As a carbon source, coal tar pitch is used.

The coal tar pitch was placed in a liquid separation bottle, and air was oxidized at 180 ° C for 2 hours while flowing 2 L/min of air. Next, fine grinding pitch was prepared by pulverizing and classifying using a jet mill. The finely ground pitch thus obtained was passed through a heated air and maintained at 280 ° C for 1 hour to carry out an oxidation treatment to obtain a porous pitch which is infusible to heat. The obtained porous pitch which was infusible to heat was preliminarily calcined at 600 ° C for 1 hour in a nitrogen atmosphere to prepare carbon precursor fine particles. Next, the carbon precursor was fired at 1200 ° C for 1 hour to obtain a carbonaceous material (negative electrode active material 1) having an average particle diameter of 15 μm. The characteristics of the obtained negative electrode active material 1 are shown in Table 1.

"Negative Active Material 2"

An easily graphitizable carbonaceous material having a sulfur content of 97 μg/g was produced. As the carbon source, a petroleum-based pitch subjected to desulfurization treatment by a catalyst is used.

A softening point of 210 ° C, quinoline insoluble fraction of 1%, H / C atomic ratio of 0.63 petroleum asphalt 68 kg and naphthalene 32 kg into a pressure vessel with a stirring blade and an internal volume of 300L, at 190 ° C Heating and melting After mixing, it was cooled to 80 to 90 ° C and extruded to obtain a rope-shaped formed body having a diameter of about 500 μm. Next, the rope-shaped formed body was crushed to have a diameter to length ratio of about 1.5, and the obtained crushed product was placed in an aqueous solution of polyvinyl alcohol (saponification degree: 88%) heated to 0.33% of 93 ° C, and stirring and dispersion were continued. After cooling, a spherical asphalt molded body was obtained. After removing most of the water by filtration, the naphthalene in the pitch molded body was removed by extraction with about 6 times the amount of n-hexane of the spherical pitch molded body.

The porous spherical pitch porous body thus obtained was heated at 180 ° C for 1 hour to carry out an oxidation treatment to obtain a porous pitch which is infusible to heat. The obtained porous pitch molded body having heat incompatibility was preliminarily calcined at 600 ° C for 1 hour in a nitrogen atmosphere, and then pulverized and classified by a jet mill to obtain carbon precursor fine particles. Next, the carbon precursor was fired at 1200 ° C for 1 hour to obtain a carbonaceous material (negative electrode active material 2) having an average particle diameter of 10.2 μm. The characteristics of the obtained negative electrode active material 2 are shown in Table 1.

"Negative Active Material 3"

A non-graphitizable carbonaceous material having a sulfur content of 121 μg/g was produced. The operation of the negative electrode active material 2 was repeated except that the temperature of the oxidation treatment at 180 ° C was 210 ° C to obtain a carbonaceous material (negative electrode active material 3). The characteristics of the obtained negative electrode active material 3 are shown in Table 1.

"Negative Active Material 4"

A non-graphitizable carbonaceous material having a sulfur content of 121 μg/g was produced. The operation of the negative electrode active material 2 was repeated except that the temperature of the oxidation treatment at 180 ° C was set to 230 ° C to obtain a carbonaceous material (negative electrode active material). 4). The characteristics of the obtained negative electrode active material 4 are shown in Table 1.

"Negative Active Material 5"

A non-graphitizable carbonaceous material having a sulfur content of 121 μg/g was produced. The operation of the negative electrode active material 2 was repeated except that the temperature of the oxidation treatment at 180 ° C was 260 ° C to obtain a carbonaceous material (negative electrode active material 5). The characteristics of the obtained negative electrode active material 5 are shown in Table 1.

"Negative active material 6"

A non-graphitizable carbonaceous material having a sulfur content of 121 μg/g was produced. The operation of the negative electrode active material 2 was repeated except that the temperature of the oxidation treatment at 180 ° C was set to 290 ° C to obtain a carbonaceous material (negative electrode active material 6). The characteristics of the obtained negative electrode active material 6 are shown in Table 1.

"Negative active material 7"

A phenolic resin was used as the carbon material to prepare a non-graphitizable carbon having a sulfur content of 300 μg/g. To 108 g of o-cresol, 32 g of polyoxymethylene, 242 g of ethyl cellosolve, and 10 g of sulfuric acid were added, and after reacting at 115 ° C for 3 hours, 17 g of sodium hydrogencarbonate and 30 g of water were added to neutralize the reaction liquid. The obtained reaction solution was poured into 2 liters of water under high-speed stirring to obtain a novolak type phenol resin. Next, 17.3 g of a novolak type phenol resin and 2.0 g of hexylamine were kneaded at 120 ° C, and heated at 250 ° C for 2 hours in a nitrogen atmosphere to obtain a cured resin. After the obtained hardened resin was coarsely pulverized, 0.5% by weight of polyphenylene sulfide was mixed. Subsequently, it was temporarily calcined at 600 ° C for 1 hour under a nitrogen atmosphere (normal pressure), and further heat-treated at 1900 ° C for 1 hour under an argon atmosphere (normal pressure) to obtain a carbonaceous material. The obtained carbonaceous material was further pulverized and adjusted to have an average particle diameter of 15 μm to obtain a negative electrode active material 7. Negative electrode obtained The characteristics of the active material 7 are shown in Table 1.

"Negative Active Material 8"

As the negative electrode active material 8, graphite derived from natural materials (manufactured in China) was used. The characteristics of the negative electrode active material 8 are shown in Table 1.

"Negative active material 9"

A carbonaceous material was prepared using petroleum pitch mixed with 3.3% by weight of polyphenylene sulfide as a carbon source.

The operation of the negative electrode active material 2 was repeated except that the temperature of the oxidation treatment at 180 ° C was 260 ° C to obtain a carbonaceous material (negative electrode active material 9). The characteristics of the obtained negative electrode active material 9 are shown in Table 1.

"Negative Active Material 10"

A phenolic resin was used as the carbon material to prepare a non-graphitizable carbonaceous material having a sulfur content of 30 μg/g. The operation of the negative electrode active material 7 was repeated except that polyphenylene sulfide was not added, and the negative electrode active material 10 was obtained. The characteristics of the negative electrode active material 10 are shown in Table 1.

"Negative active material 11"

As the negative electrode active material 11, a phenol resin (Chongfang Co., Ltd.) was used. The characteristics of the negative electrode active material 11 are shown in Table 1.

"Negative active material 12"

As the negative electrode active material 12, graphite derived from petroleum (Shenzhen Betray New Energy Materials Co., Ltd.) was used. The characteristics of the negative electrode active material 12 are shown in Table 1.

In addition, the physical property values of the carbonaceous materials described in the negative electrode active materials 1 to 12 ("average particle diameter obtained by laser diffraction method" and "average obtained by X-ray diffraction method" are described below. Method for measuring layer spacing d ₀₀₂ ′′, “crystallite thickness L _c ”, “specific surface area”, “butanol true density”, “true density”, “Li-NMR” and “sulfur content”, but includes implementation For example, the physical property values described in the present specification are based on values obtained by the following methods.

(evaluation test project) "Particle size distribution"

To the sample of about 0.1 g, 3 drops of a dispersing agent (cationic surfactant "SN WET 366" (manufactured by SAN NOPCO Co., Ltd.)) was added to dissolve the dispersing agent into the sample. Then, 30 mL of pure water was added and dispersed by an ultrasonic cleaner for about 2 minutes, and the particle diameter in the range of 0.5 to 3000 μm was determined by a particle size distribution measuring instrument ("SALD-3000J" manufactured by Shimadzu Corporation). distributed.

According to the obtained particle size distribution, the particle diameter of the cumulative volume of 50% was defined as the average particle diameter Dv ₅₀ (μm). Further, the particle diameter of the cumulative volume of 90% was set to Dv ₉₀ , and the particle diameter of the cumulative volume of 10% was set to Dv ₁₀ . Then, the value of Dv ₉₀ divided by Dv ₁₀ was set to Dv ₉₀ /Dv ₁₀ and used as an index of the particle size distribution.

"The average layer spacing d _{002 of} carbonaceous materials and the thickness of crystallites L _{c (002)} "

The carbonaceous material powder was filled in a sample rack, and measured by a symmetric reflection method using X'Pert PRO manufactured by PANalytical Co., Ltd. Under the condition that the scanning range is 8<2θ<50° and the applied current/applied voltage is 45kV/40mA, the CuKα line (λ=1.5418Å) which has been monochromated by the Ni filter is used as the line source to obtain X. Ray diffraction pattern. When the diffraction pattern is corrected, the correction of the Lorentz polarization factor, the absorption factor, and the atomic scattering factor is not performed, and the diffraction angle is corrected by using the standard material to circulate the (111) plane of the high-purity strontium powder. The wavelength of the CuKα line was set to 0.15418 nm, and d _{002 was} calculated according to the Bragg formula. In addition, the thickness of one of the half widths of the (111) ray is subtracted from the one-half width of the 002-ray ray integration method, and the thickness of the crystallites in the c-axis direction L _{c (002)} is calculated by Scherrer's formula. ₎ . Here, the calculation is performed with a shape factor K=0.9.

Specific surface area

The specific surface area was measured in accordance with the method specified in JIS Z8830. The outline is as follows.

Use derived pursuant to the formula BET of approximate formula _{v m = 1 / (v (} 1-x)), ( relative pressure x = 0.3) is calculated v _m by a single point method of nitrogen when the temperature of liquid nitrogen adsorption of, and in accordance with The specific surface area of the sample was calculated by the following formula: specific surface area = 4.35 × v _m (m ² /g) (here, v _m is the amount of adsorption (cm ³ /g) required to form a monolayer on the surface of the sample, v The measured adsorption amount (cm ³ /g), x is the relative pressure)

Specifically, using "Flow Sorb II 2300" manufactured by MICROMERITICS, the nitrogen to carbonaceous matter at a liquid nitrogen temperature was measured as follows. "Flow Sorb II2300" measures the adsorption of nitrogen on carbonaceous materials at a liquid nitrogen temperature as follows.

The carbon material was filled into the sample tube, and helium gas containing a nitrogen atomic concentration of 30 moles was flowed, the sample tube was cooled to -196 ° C, and nitrogen was adsorbed onto the carbon material. Next, the tube was returned to room temperature. At this time, the amount of nitrogen desorbed from the sample was measured by a thermal conductivity detector, and this was set as the amount of adsorbed gas v.

"Tenol true density"

The measurement was carried out using butanol according to the method specified in JIS R7212. The outline is as follows.

The internal volume of the pycnometer with a side tube of about 40 mL is correctly weighed (m ₁ ). Next, the sample was gently placed, and a thickness of about 10 mm was formed at the bottom of the pycnometer, and then the mass (m ₂ ) was properly weighed. 1-butanol was slowly added thereto to form a thickness of about 20 mm from the bottom. Next, gently vibrate the pycnometer to confirm that no large bubbles are present, and then put it into a vacuum dryer and slowly vent it to 2.0 to 2.7 kPa. Hold at this pressure for more than 20 minutes, remove the bubbles, remove them, fill them with 1-butanol, and immerse them in a constant temperature water bath (adjusted to 30±0.03°C) for 15 minutes after plugging. The level of butanol is adjusted to the mark. Next, it was taken out and the outside was wiped clean, cooled to room temperature, and then the mass (m ₄ ) was measured correctly. Then, the same pycnometer was filled with only 1-butanol, immersed in a constant temperature water bath as described above, and the liquid level was adjusted to the mark, and the mass (m ₃ ) was measured. In addition, before boiling, to remove the dissolved gas, the distilled water is taken into the pycnometer, and similarly immersed in the constant temperature water tank as described above, and the liquid level is adjusted to the mark, and the mass is measured (m ₅ ). . The true density (ρ _B ) is calculated by the following formula.

(here, d is the specific gravity of water at 30 ° C (0.9946))

"氦真密度"

When the true density ρ _H of hydrazine was used as a substitution solvent, a multi-volume pycnometer (AccuPyc 1330) manufactured by Micromeritics Co., Ltd. was used, and the sample was vacuum-dried at 200 ° C for 12 hours, and then measured. The ambient temperature at the time of measurement was fixed at 25 °C. The pressure of the measurement method is the gauge pressure, which is the pressure after the absolute pressure is subtracted from the ambient pressure.

Measuring device The multi-volume pycnometer manufactured by Micromeritics Co., Ltd. has a sample chamber and an expansion chamber, and the sample chamber has a pressure gauge for measuring the pressure in the chamber. The sample chamber and the expansion chamber are connected by a connecting pipe having a valve. A helium gas introduction pipe having a shutoff valve is connected to the sample chamber, and a helium gas discharge pipe having a shutoff valve is connected to the expansion chamber.

The measurement was carried out as follows. The volume of the sample chamber (V _CELL ) and the volume of the expansion chamber (V _EXP ) were previously determined using a standard ball. The sample was placed in the sample chamber, and the helium gas introduction tube, the connection tube, and the helium gas discharge tube of the expansion chamber were passed through the sample chamber, and helium gas was flowed for 2 hours, and the helium gas was used for replacement in the apparatus. Next, the valve between the sample chamber and the expansion chamber and the valve from the helium gas discharge tube of the expansion chamber are closed (the helium gas having the same pressure and ambient pressure remains in the expansion chamber), and the helium gas is introduced from the helium gas introduction tube of the sample chamber to After 134 kPa, close the shut-off valve of the helium gas introduction tube. After the shut-off valve was closed for 5 minutes, the pressure (P ₁ ) of the sample chamber was measured. Next, the valve between the sample chamber and the expansion chamber was opened, the helium gas was transferred to the expansion chamber, and the pressure (P ₂ ) at this time was measured.

Calculate the volume of the sample (V _SAMP ) according to the following formula.

V _SAMP =V _CELL -V _EXP /[(P ₁ /P ₂ )-1] Therefore, when the weight of the sample is W _SAMP , the true density is ρ _H = W _SAMP /V _SAMP .

Li-NMR

The prepared carbon electrode (positive electrode) and lithium negative electrode were used as an electrolyte solution for adding LiPF ₆ at a ratio of 1 mol/L in a mixed solvent of diethyl carbonate and ethyl carbonate at a capacity ratio of 1:1. A non-aqueous solvent-based lithium secondary battery was constructed using a microporous membrane made of polypropylene as a separator. Constant current flowing at a current density of 0.2 mA/cm ² until the terminal voltage reaches 0 V, and after the terminal voltage reaches 0 V, constant voltage charging is performed at a terminal voltage of 0 V, and charging is continued until the current value reaches 4 μA, which is doped in the carbonaceous material. Heterolithium. After the completion of the doping, the electrode was allowed to stand for 2 hours, and then the carbon electrode was taken out under an argon atmosphere, and the carbon electrode (positive electrode) wiped off the electrolyte was completely filled in the sample tube for NMR measurement. NMR analysis was carried out by MAS- ⁷ Li-NMR using JNMEX270 manufactured by JEOL Ltd. In the measurement, the measurement was carried out using LiCl as a reference material, and it was set to 0 ppm.

Sulfur Content

The sulfur content was measured in accordance with the method specified in JIS K0103. The outline is as follows.

10 mL of a 30% hydrogen peroxide solution was diluted with 990 mL of distilled water to obtain an absorption liquid. 50 mL of the absorption liquid was placed in two absorption bottles having a volume of 250 mL, and two absorption bottles were connected. Run the air pump to let the gas of the sample pass into the absorption bottle. At this time, the flow rate was adjusted to 1 L/min.

Move the contents of the absorption bottle to the beaker, then rinse the absorption bottle with distilled water and add the cleaning solution to the beaker. This content liquid was diluted to the quantitative range as a sample solution for analysis. The concentration of sulfur in the sample solution for analysis was measured by ion chromatography. The ion chromatograph uses a suppressor type and has a conductivity detector. Further, the column is AS-4A SC manufactured by Dionex. As a solution, a mixed aqueous solution of sodium hydrogencarbonate (1.7 mM) and sodium carbonate (1.8 mM) was prepared. The ion chromatograph was set to a measurable state, and the elution solution was flowed to the separation chromatography column at a fixed flow rate. A fixed amount of the analytical sample solution was introduced into an ion chromatograph, and the chromatograph was recorded. The sulfate ion concentration (a) (mg/mL) was calculated from the previously prepared calibration curve. The same operation was repeated for the absorption liquid, and the blank test value (b) (mg/mL) of the sulfate ion was calculated. The volume fraction (Cv) (vol ppm) of the sulfur oxide in the sample gas was calculated using the following formula using the total amount of the flask v and the sample gas taking amount Vs.

Cv = 0.233 × (ab) × v × 1000 / Vs, and the mass concentration (Cw) (mg/m ³ ) when the sulfur oxide in the sample gas is expressed as sulfur dioxide is calculated by the following formula.

Cw=Cv×2.86

"Embodiment 1"

In the present embodiment, a lithium ion secondary battery was fabricated by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 1.

A positive electrode was fabricated as follows. Into the positive electrode active material 4 obtained in the positive electrode active material production example 4, 94 parts by weight and 6 parts by weight of polyvinylidene fluoride ("KF #1100" manufactured by KUREHA Co., Ltd.) were added to NMP, and they were formed into a paste and uniformly coated. Cloth onto aluminum foil. After drying, it was punched out into a disk shape having a diameter of 14 mm by an aluminum foil, and punched by a press pressure of 392 MPa (4.0 tf/cm ² ) to prepare a positive electrode.

A negative electrode was fabricated as follows.

90 parts by weight of the carbonaceous material 1 obtained in the production example 1 and 10 parts by weight of polyvinylidene fluoride ("KF #9100" manufactured by KUREHA Co., Ltd.) were added to NMP, and formed into a paste, and uniformly applied to copper. On the foil. After drying, it was punched out into a disk shape having a diameter of 15 mm by a copper foil, and punched by a press pressure of 392 MPa (4.0 tf/cm ² ) to prepare a negative electrode. Further, the amount of the carbon material in the electrode was adjusted to about 10 mg.

Using the electrode pair thus prepared, LiPF ₆ was added as an electrolyte at a ratio of 1.5 mol/L in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:2:2. A 2032-sized coin-type nonaqueous electrolyte-based lithium ion secondary battery 1 was assembled in a St glove box using a polyethylene gasket as a separator of a microporous membrane made of borosilicate glass fiber having a diameter of 19 mm.

<<Example 2》

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 2. The lithium ion secondary battery 2 was obtained by repeating the operation of Example 1 except that the carbonaceous material 2 was used instead of the carbonaceous material 1.

Example 3

In the present embodiment, a lithium ion secondary battery was fabricated by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 3. The operation of Example 1 was repeated except that the carbonaceous material 3 was used instead of the carbonaceous material 1, to obtain a lithium ion secondary battery 3.

Example 4

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 4. The operation of Example 1 was repeated except that the carbonaceous material 4 was used instead of the carbonaceous material 1, to obtain a lithium ion secondary battery 4.

"Embodiment 5"

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 5. The lithium ion secondary battery 5 was obtained by repeating the operation of Example 1 except that the carbonaceous material 5 was used instead of the carbonaceous material 1.

"Embodiment 6"

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 6. The operation of Example 1 was repeated except that the carbonaceous material 6 was used instead of the carbonaceous material 1, to obtain a lithium ion secondary battery 6.

<<Example 7》

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 7 were combined to prepare a lithium ion secondary battery. The lithium ion secondary battery 7 was obtained by repeating the operation of Example 1 except that the carbonaceous material 7 was used instead of the carbonaceous material 1.

"Embodiment 8"

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 3 (Li ₂ Mn ₂ O ₄ ) and the carbonaceous material 5. The lithium ion secondary battery 8 was obtained by repeating the operation of Example 1 except that the positive electrode active material 3 was used instead of the positive electrode active material 4 and the carbonaceous material 5 was used instead of the carbonaceous material 1.

"Embodiment 9"

In the present embodiment, a lithium ion secondary battery is produced by combining the positive electrode active material 5 (Li _1.2 Mn ₂ O ₄ ) and the carbonaceous material 5. The lithium ion secondary battery 9 was obtained by repeating the operation of Example 1 except that the positive electrode active material 5 was used instead of the positive electrode active material 4 and the carbonaceous material 5 was used instead of the carbonaceous material 1. In addition, the producer of the positive electrode active material production example 5 was used as a positive electrode.

"Embodiment 10"

In the present embodiment, the positive electrode active material 6 (Li _1.2 CoO ₂ ) and the carbonaceous material 5 were combined to form a lithium ion secondary battery. The lithium ion secondary battery 10 was obtained by repeating the operation of Example 1 except that the positive electrode active material 6 was used instead of the positive electrode active material 4 and the carbonaceous material 5 was used instead of the carbonaceous material 1. In addition, the producer of the positive electrode active material production example 6 was used as a positive electrode.

Comparative Example 1

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 8 were combined to prepare a lithium ion secondary battery. The operation of Example 1 was repeated except that the carbonaceous material 8 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 1 was obtained.

Comparative Example 2

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 9 were combined to prepare a lithium ion secondary battery. The operation of Example 1 was repeated except that the carbonaceous material 9 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 2 was obtained.

Comparative Example 3

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 10 were combined to prepare a lithium ion secondary battery. The operation of Example 1 was repeated except that the carbonaceous material 10 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 3 was obtained.

Comparative Example 4

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 11 were combined to prepare a lithium ion secondary battery. The operation of Example 1 was repeated except that the carbonaceous material 11 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 4 was obtained.

Comparative Example 5

In the comparative example, a positive electrode active material 4 (Li _1.2 Mn ₂ O ₄ ) and a carbonaceous material 12 were combined to prepare a lithium ion secondary battery. The operation of Example 1 was repeated except that the carbonaceous material 12 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 5 was obtained.

Comparative Example 6

In the comparative example, the positive electrode active material 1 (LiMn ₂ O ₄ ) and the carbonaceous material 5 were combined to form a lithium ion secondary battery. The operation of Example 1 was repeated except that the positive electrode active material 1 was used instead of the positive electrode active material 4 and the carbonaceous material 5 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 6 was obtained.

Comparative Example 7

In this comparative example, the positive electrode active material 2 (LiCoO ₂ ) and the carbonaceous material 5 were combined to form a lithium ion secondary battery. The operation of Example 1 was repeated except that the positive electrode active material 2 was used instead of the positive electrode active material 4 and the carbonaceous material 5 was used instead of the carbonaceous material 1, and a comparative lithium ion secondary battery 7 was obtained.

"Characteristics of Lithium Ion Secondary Battery" (a) Determination of battery capacity

The lithium secondary battery was subjected to a charge and discharge test using a charge and discharge tester ("TOSCAT" manufactured by Toyo Systems Co., Ltd.). The doping reaction of lithium to the carbon electrode was carried out by a constant current and a constant voltage method, and the dedoping reaction was carried out by a constant current method. Here, in the battery using a lithium-containing chalcogen compound in the positive electrode, the doping reaction of lithium to the carbon electrode is "charging", and the dedoping reaction of lithium from the carbon electrode is "discharging". The charging method used here is a constant current constant voltage method, specifically, constant current charging is performed at a charging current value of 1 C (that is, a current value required for one hour of charging) until the terminal voltage is 4.3 V (Example 10 and Comparative Example) 7 is 4.2V), Thereafter, constant voltage charging was performed at a terminal voltage of 4.3 V (4.2 V in Example 10 and Comparative Example 7), and charging was continued until the current value reached 1/100 C. At this time, the value of the amount of electricity supplied divided by the weight of the positive electrode material of the electrode is defined as the charge capacity (mAh/g) per unit weight of the positive electrode material. After the end of charging, the battery circuit was turned on for 30 minutes and then discharged. The discharge was performed at a current value of 1 C, and the termination voltage was set to 3 V (2.75 V in the case of Example 10 and Comparative Example 7). At this time, the value of the amount of discharged electric energy divided by the weight of the positive electrode material of the electrode is defined as the discharge capacity per unit weight of the positive electrode material (mAh/g). The irreversible capacity was calculated by the charge capacity-discharge capacity.

For the test cells made using the same sample, the measured value of n=3 was averaged to determine the charge and discharge capacity and efficiency.

(b) Cycle test

A cycle test was performed on the lithium ion secondary battery obtained by the above examples or comparative examples.

First, the charging and discharging were repeated three times for the aging treatment, and then the cycle test was started. The constant current and constant voltage conditions used in the cycle test were such that charging was performed at a charging current value of 1 C until the battery voltage was 4.3 V (4.2 V in Example 10 and Comparative Example 7), and then the voltage was maintained at 4.3 V (Example) 10 and Comparative Example 7 are 4.2 V) (while kept at a constant voltage), and the current value is continuously changed, and charging is continued until the current value reaches 1/100C. After the end of charging, the battery circuit was turned on for 30 minutes and then discharged. The discharge was performed at a current value of 1 C until the battery voltage reached 3 V (2.75 V in the case of Example 10 and Comparative Example 7). The charging and discharging were repeated for 5 cycles at 25 ° C, and the discharge capacity of the fifth cycle was divided by the discharge capacity of the first cycle, which was used as a cycle. Characteristics (cycle capacity retention rate) (%). The characteristics of the obtained lithium secondary battery are shown in Table 2.

As shown in Table 2, in the positive electrode, a lithium excess chalcogenide or a combination of a lithium-containing chalcogenide compound and a Li-containing oxide is used, and in the embodiment in which a sulfuraceous material containing 75 to 3500 μg/g of sulfur is used in the negative electrode, Excellent cycle capacity retention rate of 98.0~100%. On the other hand, in the comparative example of the combination of the positive electrode and the negative electrode other than the above, the cycle capacity retention ratio was 94.9% to 97.1%. Further, in Comparative Examples 6 and 7 in which a lithium-containing chalcogen compound was used for the positive electrode and a sulfur-containing carbonaceous material in the negative electrode, the efficiencies were 78.3% and 85.0%, respectively, which were lower than those in the examples.

Industrial availability

Since the nonaqueous electrolyte secondary battery of the present invention has excellent cycle characteristics, it can be effectively used in a hybrid vehicle (HEV) and an electric vehicle (EV) which require long life and high input/output characteristics.

The invention has been described above on the basis of specific embodiments, but modifications and improvements that can be understood by those skilled in the art are also included in the scope of the invention.

Claims (3)

A nonaqueous electrolyte secondary battery comprising: (I) a positive electrode comprising (a) a formula (1): A _{x + α} M _y B _β O _z-γ (1) (wherein A is Li ⁺ , x is 1, 2, or 3, and α is 0 < α 1, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is 2, 3, or 4, γ is 0 γ 0.05) indicates a positive active material, or (b) is represented by the general formula (2): A _x M _y B _β O _z (2) (wherein A is Li ⁺ and x is 1, 2, or 3, M is one or more elements selected from the group consisting of transition metals, alkali metals, alkaline earth metals, and aluminum, and y is 1 or 2, B is P or Si, and β is 0. β 1, z is a positive electrode active material represented by 2, 3, or 4), and a lithium-containing oxide having a charge and discharge potential for the opposite electrode lithium existing at 3.3 V or less and an average discharge voltage exceeding 3.3 V of 3.4 to 5.0 V And (II) a negative electrode comprising (002) an average layer spacing d002 of 0.345 to 0.400 nm and a crystallite size Lc ₍₀₀₂₎ of the c-axis direction of 1.0 to 20.0 nm, which is obtained by an X-ray diffraction method, An easily graphitizable or non-graphitizable carbonaceous material having a specific surface area of 1 to 50 g/m ² , a butanol true density ρ _BtOH of 1.45 to 2.20 g/cm ³ , and a sulfur element content of 75 to 3500 μg/g. The non-aqueous electrolyte secondary battery according to claim 1, wherein the easily graphitizable carbonaceous material or the non-graphitizable carbonaceous material is a carbonaceous material made of pitch as a carbon source. A vehicle equipped with a nonaqueous electrolyte secondary battery as described in claim 1 or 2.